The present application is based on and claims priority from Japanese patent application 2000-32885 filed Feb. 10, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electric power equipment and, particularly, a dual voltage system for an electric vehicle that has a high voltage main DC power source and a low voltage auxiliary DC power source.
2. Description of the Related Art
A dual voltage system of a vehicle that includes a main DC power source and an auxiliary power source is already known. The main power source, such as Ni-MH battery, fuel cell or a lead acid battery is used for driving a hybrid electric vehicle, an electric vehicle or the like. In order to reduce transmission loss of the electric power, the voltage of the main DC power source is generally set as high as possible. On the other hand, the auxiliary power source is necessary to supply low voltage power to various vehicle loads.
A hybrid electric vehicle is equipped with a DC-DC converter that supplies electric power from the main power source to the auxiliary power source, which has much smaller capacity than the main power source, regularly or temporarily in an emergency. However, such a DC-DC converter complicates a control system of the dual voltage system.
Therefore, a main object of the invention is to provide an improved and inexpensive dual voltage system that has no DC-DC converter.
According to a feature of the invention, an electric power equipment includes an inverter for supplying a rotary electric machine a prescribed lower-frequency AC power from a main battery and for charging the main battery by the rotary electric machine and a main-to-auxiliary battery-power supply circuit for supplying electric power to an auxiliary battery when the terminal voltage of the auxiliary battery is lower than a reference voltage. The main-to-auxiliary power supply circuit includes a frequency filter for passing only AC power of a prescribed higher frequency that is too high for the rotary electric machine to be operated and a rectifier for converting the AC power to DC power to be charged to the auxiliary battery.
Therefore, a DC-DC converter is not necessary for charging the auxiliary battery.
Preferably, a controller for the inverter provides both the lower frequency AC power and higher frequency AC power when the terminal voltage of the auxiliary battery is lower than a reference voltage. The frequency filter preferably includes a series circuit of a coil and a capacitor having a resonance frequency. The main-to auxiliary battery power supply circuit may further include a voltage transformer having a primary coil connected to the rotary electric machine and a secondary coil connected to the rectifier.